1. Field of the Invention
The present invention generally relates to downhole cutting tools. More specifically, the present invention relates to a downhole drill bit which includes both a first and second cutting section, and methods for its use.
2. Description of the Prior Art
Conventional downhole drill bits are usually characterized by a body which defines at its proximal end a shank for attachment to a drill string and a distal end which terminates in a cutting face on which are disposed a plurality of cutting elements. Such conventional drill bits operate by boring a hole slightly larger than their maximum outside diameter. This borehole is achieved as a combination of the cutting action of the rotating bit and the weight on the bit created as a result of the mass of the drill string.
When a bore has been formed through a given formation, the rock immediately surrounding the borehole is in many instances quite frangible as a result of the decompression of this surrounding rock. Such decompression of the surrounding country rock has traditionally been viewed as a nuisance, necessitating casing of the borehole.
The present invention is directed to a two stage drilling tool which comprises a body defining a proximal end and a distal end, where said proximal end defines a shank for attachment to the drill string. The distal end defines a first drilling face having a certain outside diameter, which first face is disposed above and set apart from a second drilling face having a larger outside diameter, where both the first and second diameters are provided with gauge pads to stabilize the bit in the borehole.
The drill bit of the invention offers a number of advantages. One such advantage is enhanced stability of operation. A second advantage is increased rate of penetration as a result of the decompression of the rock effected by the smaller, first drilling face.